Using a developmental bioassay in which the clearance from the lung of intravenously injected radiolabelled tumor cells is measured, we propose to compare the anti-tumor activity of a variety of reticuloendothelial stimulants. Specifically the optimum doses, time for the genesis of anti-tumor effects, the optimum time points for, and length of time such effects last, will be established in normal "immunologically naive" mice and in mice bearing spontaneously metastasizing tumors, for various forms of BCG, C. parvum, Glucan, Pyran co-polymers, MDPs, and Lipopolysaccharide B.